The Dynamic Host Configuration Protocol (DHCP) provides a mechanism to dynamically specify an IP address and other configuration parameters of a host. In a network where the location of a host frequently changes, DHCP allocates and manages IP addresses and other parameters of hosts dynamically. When a host joins a network, the host can obtain an IP address and other parameters dynamically from a DHCP server in the network and establish a channel automatically for communication with other hosts.
DHCP is available in two versions, v4 and v6, which serve in IPv4 and IPv6 networks respectively. DHCPv6 may be stateful and stateless. In the stateful mode, a terminal obtains an IP address and other configuration information simultaneously from a DHCPv6 server. In the stateless mode, a terminal obtains only some state-unrelated information, like domain name server (DNS) information, from a DHCPv6 server after obtaining an IP address manually or by other means.
In a mobile IP network or a NEMO (Network Mobility, NEMO), a mobile node (MN) may first obtain a home address from a DHCP server and register the home address in a home agent. When the MN moves from a home link to a foreign link, the MN can obtain a care-of address automatically from a stateful or stateless DHCP server and register the care-of address in the home agent. Thus, the MN and a correspondent node can communicate over a bidirectional tunnel or through route optimization. Therefore, the basis for an MN to continue with subsequent interactions is that the MN obtains the IP address information of a home agent.
The current method defined in Request For Comments (RFC) for obtaining the home agent address is: when the MN does not know the home agent address or when the home agent address changes, that is, after the MN obtains the care-of address, the MN sends a Home Agent Discovery message to anycast addresses of mobile IPv6 home agents, or broadcasts a Home Agent Discovery message over mobile IPv4; the home agent receives the Discovery message and sends a response message to the MN; the MN extracts the address information of the home agent of the MN from the response message.
RFC defines only the method for obtaining the home agent address through a Home Agent Discovery message after the MN obtains the care-of address. It does not define a method for an MN to obtain the home agent address when the MN is started up on a home link. In addition, after the MN obtains the care-of address, the MN needs to exchange many messages with the home link to obtain the home agent address. This compromises the handover speed of the MN.